The Public Switched Telephone Network (PSTN) has undergone tremendous advancement since its inception. Fibre-optic cables and satellites can simultaneously carry an enormous number of telephone calls. The Signaling System #7 (SS7) protocol and the Advanced Intelligence Network (AIN) provide support for a number of enhanced calling features such as call forwarding, voice mail and the like. Notwithstanding these advancements, at its essence the PSTN still establishes a telephone call between subscribers by completing a connection between subscriber's telephone lines, which, as a circuit-switched network, makes the current PSTN notionally identical to the way calls were completed when the PSTN was first conceived. Inherent in the PSTN architecture is the paradigm that each subscriber is uniquely associated with a physical telephone line. Thus, a subscriber's telephone number and the calling features preferred by the subscriber are also uniquely associated with the same physical telephone line, which can constrain the creation of additional enriched features that would be otherwise supported by modern technology.
For example, the unique association between a subscriber and a telephone line creates problems when implementing local-number portability, although SS7 does offer certain ways to implement local-number portability within the existing PSTN. Furthermore, calling features, such as caller-id and call-waiting, can only be accessed at the subscriber's phone line—thus if the subscriber is using another telephone line the subscriber may not have access to these features.
Another limitation with the PSTN structure relates to typical implementations of the call-forwarding feature. Due to the unique association between one subscriber and one telephone line, when a first subscriber forwards his telephone line to a second subscriber's telephone line, a caller for the first subscriber may be confused when the second subscriber answers. In any event, while the first subscriber's phone is forwarded, the caller will not be able to leave a message on the first subscriber's voicemail, nor will anyone using the first subscriber's telephone be able to receive an incoming telephone call, as all such calls will forward to the second subscriber's telephone.
More flexibility in network architectures can be found outside the PSTN. For example, in WO-9925071-A2, a data network architecture is taught that allows users to access data from the network via different types of client devices (e.g. computer terminals, cell-phones, or personal digital assistants) that are connected in a distributed manner to the network. WO-9925071-A2 teaches a database in the network which stores client device capabilities, and a second database in the network that contains user profiles. When a user accesses a particular client, the network first determines the capability of the client, and then determines the services to which the user subscribes, granting access to the user based on the subscribed services making appropriate format conversions in data to allow presentation of accessed data on the client device. However, WO-9925071-A2 is limited to non-real time services such as the accessing of email or web-browsing. While WO-9925071-A2 does contemplate some types of voice services (i.e. the retrieval of voicemail or text-to-speech conversions of email), WO-9925071-A2 does not teach a network that manages end-to-end real-time applications, such as voice telephone calls, such that WO-9925071-A2 does not present a viable alternative to the PSTN.
Overall, it can be seen that the existing network architecture constrains the elegant implementation of certain enriched features, and it desirable to provide a novel structure that readily supports such features.